For more than two years, Facebook CEO Mark Zuckerberg has touted membership in private, “meaningful” communities as central to the future of the social network.

But that strategy of pushing closed interactions within groups is increasingly butting up against the company’s capacity to monitor those that break the social network’s rules against hate speech, harassment and other ills, civil rights groups and other advocates say. They warn that the company’s move into more private communications is on a collision course with Facebook’s stated goal of cleaning up its platform before the 2020 U.S. presidential election.

Facebook’s failure to monitor problematic groups surfaced again last week after an investigation by ProPublica revealed that a secret, members-only group of current and former Border Patrol agents joked callously about the deaths of migrants and used a vulgar illustration of Rep. Alexandria Ocasio-Cortez, D-N.Y.

The company said Friday that it also removed several problematic posts from another Border Patrol group.

The pattern of not policing private groups — which Facebook said are subject to the same rules as other parts of the social network — has become a bigger concern as the company pushes those channels as a key piece of how it wants people to use its site.

“Large private groups remain unmoderated black boxes where users can freely threaten vulnerable populations,” said Jonathan Greenblatt, chief executive of the Anti-Defamation League. “Without any AI or human moderators, it’s easy to orchestrate harassment campaigns — at minimum, this environment contributes to the normalization of bigotry and discrimination. As Facebook moves to more and more private communication, we’re concerned about this delinquency.”

Zuckerberg has been pushing a plan to transform Facebook into a group-oriented platform that would transition it from a “town square” of public news feeds into more of a “living room” designed around personal interactions with family and friends.

It is not Facebook’s first run-in with private groups that violate its policies. The company declined to provide details on its interaction with the private groups and said it was cooperating with authorities. A spokeswoman said the company uses a combination of technology and human review to remove rule-breaking content, including in secret groups.

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